flatten() public

Returns a new array that is a one-dimensional flattening of this array (recursively). That is, for every element that is an array, extract its elements into the new array. 

   s = [ 1, 2, 3 ]           #=> [1, 2, 3]
   t = [ 4, 5, 6, [7, 8] ]   #=> [4, 5, 6, [7, 8]]
   a = [ s, t, 9, 10 ]       #=> [[1, 2, 3], [4, 5, 6, [7, 8]], 9, 10]
   a.flatten                 #=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10
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May 5, 2020
0 thanks

Make your custom enumerable "flattenable"

Just alias to_a to to_ary

class A
  include Enumerable

  def each
    yield "a"
    yield "b"
  end
end

[A.new, A.new].flatten => [#<A:0x00007fbddf1b5d88>, #<A:0x00007fbddf1b5d60>]

class A
  def to_ary
    to_a
  end
end

[A.new, A.new].flatten => ["a", "b", "a", "b"]